Group touts graphene transistor advance

LONDON  Researchers at the University of Manchester (England) have unveiled what they claim is the smallest transistor made, measuring one atom thick and ten atoms across.

The breakthrough, revealed in the latest issue of Science magazine, breaks the same team's record for a transistor made from graphene, revealed last year, which measured 100-nm across.

Made of intricately linked carbon atoms, graphene has the ability to retain several important properties when only one atom thick -- most importantly conductivity. The material exhibits exceptionally high crystal and electronic quality, and the researchers claim has numerous potential applications in condensed matter physics and electronics.

Last month, scientists at the University of Maryland in the U.S. said they had characterized graphene monolayers that were of pure carbon just one atom thick. They discovered that graphene appears to be unfazed by temperature, unlike most semiconductors.

The Manchester group created the transistors using standard semiconductor fabrication technology. They begin with a small sheet of graphene and carve channels into the material using electron beam lithography. What remains is a quantum dot with a tiny circular cage at the center known as the central island. Voltage can change the conductivity of these quantum dots, allowing them to store logic states just like standard field-effect transistors.

The work is being led by Dr Kostya Novoselov and Professor Andre Geim from The School of Physics and Astronomy at Manchester University, and the latest advance shows graphene can be carved into tiny electronic circuits with individual transistors having a size not much larger than that of a molecule.

However Dr Novoselov cautioned that it is currently impossible to produce large amounts of graphene. They can only produce graphene crystals about 100 microns across, too small for industrial production.

"Probably this problem will be solved in the next couple of years," he said.

The major drawback is the poor stability of materials if shaped in elements smaller than 10 nanometres in size. At this spatial scale, all semiconductors 
including silicon  oxidize, decompose and uncontrollably migrate along surfaces like water droplets on a hot plate.

Four years ago, Geim and his colleagues at Manchester were one of the first teams to describe graphene, the first known one-atom-thick material which can be viewed as a plane of atoms pulled out from graphite. Since then graphene has become one of the hottest topics in semiconductor materials science.

"Previously, researchers tried to use large molecules as individual transistors to create a new kind of electronic circuits. It is like a bit of chemistry added to computer engineering", says Novoselov. "Now one can think of designer molecules acting as transistors connected into designer computer architecture on the basis of the same material (graphene), and use the same fabrication approach that is currently used by semiconductor industry."

Geim added: "It is too early to promise graphene supercomputers. In our work, we relied on chance when making such small transistors. Unfortunately, no existing technology allows the cutting materials with true nanometre precision. But this is exactly the same challenge that all post-silicon electronics has to face. At least we now have a material that can meet such a challenge."

"These transistors will work and work at ambient, room temperature conditions - just what is required for modern electronics," he said.
Geim adds graphene is "superior" to silicon by an order of magnitude and comparable to the best samples of other materials and that the process of using graphene to build circuits was very compatible with silicon technology.

"At the moment we use all the same steps to make a transistor as is done by the silicon industry. So once we have large wafers of graphene it should be straightforward to use the same process."

But Grim suggested it might be another 10 years before the first integrated circuits on graphene chips start appearing , and noted the material could be used earlier in LCD displays to replace materials used to create transparent conductive coatings.